Production of chromate



Patented Jan. 10, 1950' UNITED STATES PATENTTOFFICE 2,493,789. I 1 I PRODUCTION OF CHROMATE Marvin J. Udy, Nia ara Fal1s, N ;Y; No Drawing. Application'August 14,V194s,

Serial No. 44 399;

14 Claims. (Cl. 23-56)' This invention relates to chromate production and has for an object the provision of an improved process for producing calcium chromate. The invention further contemplates the provision of an improved process for recovering chromium in the form of calcium chromate from chromite ore, chromite ore concentrates, altered chromite ore and similar chromium-bearing material's.

Throughout the specification and in the claims, the term chromite ore is intended to include natural chromite ore, altered chromite ore, chromite ore concentrates and similar chromite mineral-bearing materials.

According to some heretofore customary practices,"chromite ores are subjected to oxidizing or roasting treatment in the presence of one or more alkali metal compounds suchyfor example, as sodium carbonate, sodium hydroxide and sodium sulphate under such conditions as to oxidize the trivalent chromium of the chromite ores to the hexavalent state and produce alkali meta1 chromates such, for example, as sodium chromate. Sodium chromate thus produced is separated from the product of the roasting or oxidizing treatment by leaching and crystallization and marketed as such or converted to sodium dichromate 'IOI marketing. Commercial sodium chromate and sodium dichromate are utilized as raw or intermediate materials in the production of other chromium-bearing compounds, including calcium chromate. Usually, the calcium chromate production operations are carried out independently of the sodium chromate production operations and, consequently, the sodium oxide content of the sodium chromate is wasted or, at any rate, is not recovered in a form in which it is readily available for re-use in the chromate production operations. For this reason, among others, calcium chromate is a relatively costly commercial product. Calcium chromate is a highly desirable material for many industrial uses, but its usefulness has not been developed fully because of its high cost.

The present invention provides for the production of calcium chromate under conditions and according to procedures such that the sodium oxide content of sodium chromate employed in its production is utilized for the production of addi- The-two procedures arecombined with advantage they may-be represented by the following equations for purposes of illustration:

(1) 4NaCl+ LNH4I-ICO =4NaHCOs+4NH4Cl 2) CI'2O3+4N aI-ICO3+1 O2= j v 2Na2 CrQ4+2I-I2CO3+2 CO2 (3) 2NaaCrO4-i 2CaClz:2CaCrO4+4NaCl on znmc g zca(on) =4mn+ zoacn+ imo The 'foregoin'gequations illustrate the principal reactions.- The -following'equations illustrate additional reactions involvedin the process Acomplete preferred process of the invention comprises (:1) reacting sodium chloride and ammonium bicarbonate to produce sodium bi carbonate'and ammonium chloride, (2) regenerating the ammonium bicarbonate by'reacting the ammonium chloride with calcium hydroxide with the production of ammoniaand calcium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid, (3) producing "calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with'the sodium'oxide of the sodium bi carbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with thecalcium chloride produced in regenerating the ammonium bicarbonate, (4) separating the calcium chromate from the regenerated sodium chloride, and (5) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate. I

-As in the operation of the ammonia soda process to produce sodium bicarbonate as an end product; the production of sodium bicarbonate by reaction of sodium chloride and ammonium bicarbonate preferably includes the step of ammoniation of the, sodium chloride-containing brine,,the step of carbonating the ammoniated brine, and separation of the solid sodium bicarboing the roasting in air of finely divided chromite ore in the presence of available sodium oxide. The sodium? oxide may be produced-by employing sodium bicarbonate directly or by employing soda ash produced through decomposition of the sodium bicarbonate. The efiect is the same whether:

sodium bicarbonate or soda ash is employed.. The.

sodium bicarbonate or soda ash is employed in amount suflicient'to provide sodium-oxidefor;v

combining with all of the chromium of the chromite ore when converted to the hexavalentstate" The sodium bicarto form chromium trioxide.

bonate or the soda ash is mixed intimately with;

the chromite ore of thef roasting charge, and the charge is heated w a. temperature inthe range '7 50- G. tollOO G. In the course of: the heating operation in the presence of.-air,. the sodium bisolution of sodium chromate" may be employedin the calcium-chromate production. step directly, or the solution of sodium chromate may be concentrated or. evaporatedlto dryness to. produce either a concentrated solution or a solid product for use in the calcium chroma-te production step;

The sodium chromate preferably is added to the calcium chloride-containing solution; which corresponds to the distiller waste solution. of the ammonia soda process, while the solutioncontainsthe heat absorbed in the distillation operation. Incidentally, the distiller waste solution also contains the sodium chloride not utilized in the conversion to sodium bicarbonate. Thecalcium chloride-containing solution to which the sodium chrom'ate is added preferably isiheated to a. temperature equivalent atleast to: the boiling. temperature at atmospheric. pressure, and it'pref erably is heated to a temperature in: the range,- 126 C. to 135 C., under a pressure; in the range, 15 to 30 pounds per square inch, toeffect precipitation of anhydrous calcium chromate At temperatures and pressures in the ranges indicated, precipitationv of. calcium chromatevirtual ly is complete. Complete removalof the calcium; chromate is notessential to the economy of the process, as the mother liquor from the precipitation treatment is to be ire-cycled to regenerate sodium. bicarbonate, and chromate remaining therein will not interfere with the reactions involved in the ammonia soda process. The chromate will remain in the system without loss. When equilibrium has been established, calcium-. chromate equivalent to the sodium chromateem- 7 ployed will be obtained at aiuniformrate. The":

advantage resulting from avoidance of the neces- The mother liquor may be subjected to an evaporation concentration treatment or not, depending upon the amount of dilution water employed in the process. In the ammonia soda process designed and operated for the production of a sodium bicarbonate product for marketing as such, dilution water may be introduced at two points, namely, at the filters as wash water for the' rsodium bicarbonate, and in the distiller in the f orm ofmilk. of lime. In the process of the invention, washing of the sodium bicarbonate at the filters is unnecessary because the crude product can beem'ployed directly in the chromate production step, and, if desired, the lime may be added in; the solid state to the distillers to avoid the introduction of water into the system. In

j the'process of the invention, diluent water may beadded with the sodium chromate, but addition at; this point can be avoided by employing the sodium chromate in the form of a solid. If the addition of diluent water through washing and reagent addition is eliminatedcompletely, it will belnecessaryto add make-up water to compensate .-fo r evaporation. In any event the function;- ingzof the processot the'invention. can be so con.- trolled that evaporation costs will be slight or even negligible. 7

The combined usev ot-the principles and reactionsof the ammoniasoda process and the principles-and reactions of a. calcium chromate-product-ion process permits the achievement of the fol-lowing advantages, among others:

(1) It permits re-use of the brine with a: saving in. cost of raw materials, a saving in the cost' of preparing and; purifying the brine and with; the establishment of more uniform conditions leading to greater .efliciency through the use of brine ofi the-sameacomposition in all, am'moniation and carbonation operations." l

1(2) Itperm'its the-saving and utilization: in the production of the endiproduct of the combined process .of calcium chloride which normally is wasted in the: ammonia sodaprocess.

p (3); It conserves the heat of the distiller waste solution which normally is dissipated without ac complishinga useful; result or is used inefficiently, and, itpermits utilization of the heat directly in:

the production of theend'product of: the combined:

process.

- 4) It permitsa saving in labor and. equipment:

7 costs by permitting elimination of. washing ofthe sodium bicarbonate at the. filters.

..I claim: 1 1 :1- A cyclic processfcr producing calcium chromate which comprises ('l) reacting sodium chloride and. ammonium bicarbonate to produce sodium bicarbonate and ammonium chloride, ('2). regenerating the ammonium. bicarbonate byre acting the ammonium chloride with calcium hy-'- sity for complete elimination of the chromate fardroxide with the production of ammonia and cal-- cium chloride and by reacting the ammonia thus produced with "carbon dioxide in an. aqueous: liquid, (3) producing calcium chromate and simultaneously regenerating" the sodium chloride by reacting chromic' oxide withthe sodium oxide: of thesodi'um bicarbonate under oxidizing. con ditions, to formsodium chromate and reacting the-sodiumchromate with: the calcium chloride produced in regenerating theiammonium bicarbonate, (4') separating the calcium chromate ate-sodium bicarbonate for use in the productionof v additional calcium chromate.

monium chloride, (2) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production ofammonia and calcium chloride and by reacting theammonia thus produced with carbon dioxide in an aqueous liquid, f

(3) producing calcium chromate and simultaneously regenerating the sodium chloride by re: .acting chromic oxide with the; sodium oxide of the. sodium bicarbonate underoxidizing conditions to form sodium chromate and reacting the r sodium chromate with-the calcium chloride produced in regenerating the ammonium bicarbonate at an elevated temperature, (4) separating the calcium chromate from the regenerated sodium chloride, and utilizing the regener ated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate.

3. A cyclic process for producing calcium chromate which comprises (1) reacting sodium chloride and ammonium bicarbonate in aqueous solutionto produce sodium bicarbonate and ammonium chloride, (2) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production of ammonia and calcium chloride and by reacting the ammonia thus produced with carbon. dioxide in an 1 aqueous liquid, (3) producing calcium chromateand simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide ofthe sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution at a boiling temperature, (4) separating the calcium chromate from the regenerated sodium chloride, and (5) .utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional. calcium chromate.

.. 4. A cyclic process for producing calcium chromate which comprises (1) reacting sodium chloride and ammonium bicarbonate in aqueous solution to produce sodium bicarbonate and ammonium chloride, (2) regenerating the ammo,- nium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production of ammonia and calcium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid, (3) producing calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution under pressure at a temperature above 100 C., (4) separating the calcium chromate from the regenerated sodium chloride and (5) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in .the production of additional calcium chromate. 5. A cyclic process for producing calcium chro- "mate which comprises (1) reacting sodium chloride and ammonium bicarbonate in aqueous solution to produce sodium bicarbonate 'andfammonium chloride, 2) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous. solution withthe production of ammonia and calcium chloride and by reacting the ammonia thus produced with 'carbon dioxide in an 5 aqueous liquid, (3) producing calcium chromate and simultaneousiy regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of, the sodium bicarbonate under oxidizing con- .ditions toform sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in, aqueous solution under pressure above pounds per square inch atra temperature above 120 C., (4) separating the calcium chromate .from the regenerated sodium chloride and (5) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate-sodium bicarbonate for use inthe production of additional calcium chromate. I 6. A' cyclic process for producing calcium chromate which comprises (1) reacting sodium chloride and ammonium bicarbonate in aqueous solution to produce sodium bicarbonate and 'ammonium chloride, (2) regenerating, the. ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production of ammonia and calcium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid; (3) producing calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with the calcium chloride produced in, regenerating the ammonium bicarbonate in aqueous solution under pressure at a temperature in the range 120 C. to 135 C., (4) separating the calcium chromate from the vroegenerated sodium chloride and (5) utilizing the regeneratedsodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate. V '7. A cyclic process for producing calcium chromate which comprises (1) reacting sodium chloride and ammonium bicarbonate. in aqueous solution to produce sodium bicarbonate and ammonium chloride, (2) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production .of ammonia and calcium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid, .(3) producing calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution under pressure in the range 15 to pounds per square inch, at a temperature in the range, 120 C. to 135 C., (4) separating the calcium chromate from the regenerated sodium chloride and (5) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate forum in the production of additional calcium chromate.

-8.1 A cyclic process for producing calcium chromate which comprises (1) reacting sodium chlo- 75 ride and vammonium bicarbonatev to: produce produced with carbon dioxide in-anaqueous liquid,

K39 producing calcium :chromate and simultaneousl-yregenerating thesodi-umchioride byreacting chromic oxide with t-he sodium oxide of the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium zchromate with the calcium chloride produced'in regenerating the ammonium bicarbonate, (4)

p separating the calcium .chromate from the rogramerated sodium chloridaand (5-) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate, the reaction between the chromic (oxide and thezsodium oxide of the bicarbonate being effected-by roasting'a mixture comprising chromite ore andthe sodium oxide in air at a temperaturein the range 750 0.1130 1100' C.

9. A cyclic process for producing calcium chromate which comprises -(1) reacting sodium chloride and ammonium bicarbonate aqueous solution to produce sodium bicarbonate and am- 'monium chloride, (2) regenerating the am- -monium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous'solution with the production of ammonia and cal- :zcium chloride and :by reacting the .ammonia thus produced with carbon dioxide in an aqueous (39 producing calcium r-c'hromate and is'i- :multaneously regenerating the sodium :chloridez:

by reacting .chromic oxide with-the'sodiumnoxide f thesodium.-1: icarbonate underoxidizing conditions to form sodium .chromate and reacting --the sodium chromate with the'calcium chloride produced in regenerating the ammonium bicarbonate at an elevated temperature, 14') -separating the calcium chromate from the regeneraated sodium chloride, and utilizing the regenmated sodium chloride and i the regenerated am- -monium bicarbonate Ito regenerate .sodiumxbicarbonate :ior use in the production of additional calcium chromate, the reaction between the chromic ioxide and the sodiunimrid'elzof the bi- -carbonate .zbeing effected by :roasting :a mhdtmie comprising chromite :ore and the :sodiummrdde 1 "in air at a temperature "in :the range 3750 Cr-lto 1160:C.. A i

.10. A cyclic process for producing ecalcium rchromate which comprises (1) reactingrsodium .-chloride and ammonium .ibicarhonateo'in aqueous solution "to produce :sodium bicarbonate and amjmonium chloride, (2) regenerating the 1am- -monium bicarbonate: by reacting the :ammonium chloride with calcium hydroxide aqueous-solu- 'tion with 'the/ productionliqf ammonia and cal- :cium chloride and vby reactingiithe: ammonia ithus zproduced with carbon dioxide in van aqueous diquid, (-3) producing calcium "chromate' zmd .s'i

multaneously regenerating the sodiumichzluridezfiby reacting chromic oxide WithJ-the sodium aOXi'dB of the sodium bicarbonate .under oxidizing conditions :to form. sodium chromate and reactingthe sodium chromate' with the calcium chloride prosduced .in regenerating theammonium bicarbonate --in ;a'queous solution ate-a z-boiling temperature, (4. separating the calcium chromate'from the regen .erated sodium chloride. and (5) utilizing git-he regenerated sodium chloride the z regenerateii ammonium rsbicarbonate m) regenerate bicarbonate ioriuse in f the production of "additional calcium chromate, the react-ion between the chromic oxide and the sodium oxide oi the bicarbonate being effected by reacting a mixchromate which comprises (1) reacting sodium "chloride and ammonium bicarbonate in aqueous SOlll-i'ilOll to produce sodium bicar'bona te and ammonium -chloride, (2-) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous-solution with the production of ammOnia-and'caIGium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid, (-3) producing calcium chromate and simultaneou'sly regenerating the sodiumch l'oride by reacting chromic oxide with the-sodium "oxide of :the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium 'chromate with the calcium chloride produced regenerating the ammonium bicarbonate in aqueous solution under pressure at a temperature above 13., i4) separating the calcium chromate from the regenerated sodium chloride and (5) utilizing the regeneratedsodiumchloride-arid the regenerated ammonium bicarbonate to regen- --er.ate sodium bicarbonate for use inthe production of additional calcium chromate, the reaction between the chromic .oxide and the-sodium oxide "of the bicarbonate being eiiected -by roasting a mixture comprisingchromite ore-and the sodium oxide in air at a temperature in the range'fl50 0. 1201100 0. V r .112 A cyclic process :iior producing calcium chromate which comprises (1') reacting sodium chloride and U ammonium -bicarbonate in-aqueous solution to produce sodium-bicarbonate and-amvmoniumrchloride, (2) regenerating the-ammonium bicarbonateibyreacting the ammonium chloride with calcium hydroxide in-a'queous solution "with :the production of ammonia and calcium --c'hloride I anduby reacting the ammonia thus pro duced with carbon dioxide in an aqueous liquid, ('3) producing calcium chrom-ate and simultan fl-eously regenerating the sodium chloride' byreacting chromic oxide with-the-sodiumoxide cf the sodium bicarbonate under oxidizing conditions tc-form sodium chromaterand reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution under pressure above "15 pounds :per square inch at a temperature above 0;, (4) separating the calcium chromate from the regenerated sodium 'chlorideand (5-) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate so- -dium bicarbonate ioruse in the production of additional calcium chromate, --=the reaction between the chromic' oxide and the sodium-oxide of the bicarbonate being eliected by roasting a mixture comprising chromite ore and the sodium oxide in air at a temperature in the range750C. to 1100 C. r A cyclic process for producing calcium chromate which comprises (-1) reacting sodium chloride and ammonium-'bicaflaonate in aqueous solution to produce sodium bicarbonate and animonium chloride, (2) regenerating the fammonium bicarbonate by reacting'tjhe ammonium chloride with calcium hydroxide in aqueous solution with the -production of ammonia and calcium 7 (3) producing calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of the sodium bicarbonate under oxidizing conditions to form sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution under pressure at a temperature in the range 120 C. to 135 C., (4) separating the calcium chromate from the regenerated sodium chloride and utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate, the reaction between the chromic oxide and the sodium oxide of the bicarbonate being efiected by roasting a mixture comprising chromite ore and the sodium oxide in air at a temperature in the range 750 C. to 1100 C.

14. A cyclic process for producing calcium chromate which comprises (1) reacting sodium chloride and ammonium bicarbonate in aqueous solution to produce sodium bicarbonate and ammonium chloride, (2) regenerating the ammonium bicarbonate by reacting the ammonium chloride with calcium hydroxide in aqueous solution with the production of ammonia and calcium chloride and by reacting the ammonia thus produced with carbon dioxide in an aqueous liquid, (3) producing calcium chromate and simultaneously regenerating the sodium chloride by reacting chromic oxide with the sodium oxide of the sodium bicarbonate under oxidizing conditions to 10 form sodium chromate and reacting the sodium chromate with the calcium chloride produced in regenerating the ammonium bicarbonate in aqueous solution under pressure in the range, 15 to 30 pounds per square inch, at a temperature in the range, C. to C., (4) separating the calcium chromate from the regenerated sodium chloride and (5) utilizing the regenerated sodium chloride and the regenerated ammonium bicarbonate to regenerate sodium bicarbonate for use in the production of additional calcium chromate, the reaction between the chromic oxide and the sodium oxide of the bicarbonate being efiected by roasting a mixture comprising chromite ore and the sodium oxide in air at a temperature in the range 750 C. to 1100 C.

MARVIN J. UDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS facture of Soda, (1933) 

1. A CYCLIC PROCESS FOR PRODUCING CALCIUM CHROMATE WHICH COMPRISES (1) REACTING SODIUM CHLORIDE AND AMMONIUM BICARBONATE TO PRODUCE SODIUM BICARBONATE AND AMMONIUM CHLORIDE, (2) REGENERATING THE AMMONIUM BICARBONATE BY REACTING THE AMMONIUM CHLORIDE WITH CALCIUM HYDROXIDE WITH THE PRODUCTION OF AMMONIA AND CALCIUM CHLORIDE AND BY REACTING THE AMMONIA THUS PRODUCED WITH CARBON DIOXIDE IN AN AQUEOUS LIQUID, (3) PRODUCING CALCIUM CHROMATE AND SIMULTANEOUSLY REGENERATING THE SODIUM CHLORIDE BY REACTING CHROMIC OXIDE WITH THE SODIUM OXIDE OF THE SODIUM BICARBONATE UNDER OXIDIZING CONDITIONS TO FORM SODIUM CHROMATE AND REACTING THE SODIUM CHROMATE WITH THE CALCIUM CHLORIDE PRODUCED IN REGENERATING THE AMMONIUM BICARBONATE, (4) SEPARATING THE CALCIUM CHROMATE FROM THE REGENERATED SODIUM CHLORIDE, AND (5) UTILIZING THE REGENERATED SODIUM CHLORIDE AND THE REGENERATED AMMONIUM BICARBONATE TO REGENERATE SODIUM BICARBONATE FOR USE IN THE PRODUCTION OF ADDITIONAL CALCIUM CHROMATE. 